Aluminum bronze alloys



Patented Sept; 14, 1937 ALUMINUM BRONZE ALLOYS Alan Morris,

Bridgeport,

Conn., assignor to Bridgeport Brass Company, Bridgeport, Conn., a corporation of Connecticut No Drawing. Application June 12,1936, Serial No. 84,872

5 Claims. (Cl. -162) This invention relates to corrosion resistant copper alloys for condenser tubes, heat exchanger tubes and the like.

The purpose of this invention is to provide a copper alloy highly resistant to the various types of corrosive attack experienced in the use of metal tubes in surface condensers and analogous devices, including resistance specifically to what is known as air impingement corrosion and to localized pitting.

Brass alloy tubes, containing considerable percentages of zinc, have been most commonly used in the past for this purpose. Among the types of corrosive attack most commonly experienced in the use of brass alloy tubes are:-

. General dezincification.

. Plug type dezincification.

. General thinning.

Air impingement attack.

. Deposit pitting.

. Localized pitting or "pin hole attack".

Types 1 and 2 are experienced only in tubes containing zinc. This form of attack is characterized by the spongy copper left in place of the alloy removed by corrosion. It is of course not met with in the use of alloys containing no zinc.

Type 3. General thinning is the result of chemical attack accompanied by removal of the products of corrosion.

Type 4. Air impingement attack results from the breaking down and removal of the natural protective film of corrosion products by the impingement on the tube surface of air bubbles in the cooling water stream. The extent and rapidity of this type of corrosion depends upon such variables as the temperature of the water, the

amount of air in the water, the size of the bubv bles, the velocity of the water and its turbulence, and the chemical composition of the salts and gases in solution in the water. Of course alloys differ in their inherent resistance to this form of attack. x

Type 5. Deposit pitting takes place when a foreign body lodges in a tube.

Type 6. Localized pitting, sometimes called pinhole attack, is characterized by the formaherently superior to brass alloys containing considerable percentages of zinc.

They are fairly resistant to general thinning, deposit pitting and air impingement attack, but fail rapidly when conditions of service are such as to develop the localized pitting type of corrosive action.

I have found by incorporating into the aluminum bronze a small percentage of arsenic, the resultant alloy is not only rendered more resistant to air impingement type of corrosion, but particularly its resistance to localized pitting is very markedly improved. These new aluminum bronzes containing arsenic are useful for making into condenser tubes, heat exchanger tubes and other articles and fittings subject in use to the aforesaid types of corrosive attack.

In said new alloys, the copper may vary from approximately 98.0 to 91.0% and the aluminum may vary from approximately 2.0 to 9.0% and there will be a small percentage of arsenic. The optimum percentage of arsenic is about 0.2%. However, the arsenic ingredient may vary from about 0.01 to about 0.5% and still secure good protection against corrosion.

The following are specific examples of alloys within the invention which are remarkably resistant to air impingement corrosion and localized pitting and are otherwise very suitable for making into condenser tubes and other articles that are subject to corrosion as aforesaid:

1. An alloy composed of approximately 5.0% aluminum, 0.4% arsenic, with the balance consisting substantially entirely of copper.

2. An alloy composed of approximately 6.0% aluminum, 0.2% arsenic, with the balance consisting substantially entirely of copper.

3. An alloy composed of approximately 5.0% aluminum, 0.1% arsenic, 0.5% tin, with the balance consisting substantially entirely of copper.

Small percentages of other metals are permissible as impurities or may be added to impart special characteristics without substantially changing the highly. resistant characteristic of these alloys to corrosion.

For example, under the heading of impurities, there may be permitted the following: iron, silicon, tin, nickel, magnesium.

Under "added metals the following may be used for purposes and with advantages respectively as follows:

Manganese, phosphorus, silicon may be added in small amounts, up to about 0.1%, for fluxing action in casting, thereby obtaining sounder castings.

Tin, nickel, cobalt, magnesium. silicon may be added in small amounts, from about 0.5 to 2.0%, for added resistanceto corrosion.

Iron may be added for the purpose oi increasing strength and hardness and refining the grain without materially reducing the ductility.

What I claim is:

1. A corrosion resisting alloy containing approximately 2.0 to 9.0% aluminum, 0.01 to 0.5%

arsenic, and the remainder copper. 1

2. An alloy resistant to air impingement corrosion and localized pitting which contains about 6.0% aluminum, 0.2% arsenic and the remainder copper.

3. A corrosion resisting alloy containing approximately 2.0 to 9.0% aluminum, 0.2% arsenic and the remainder copper.

' 4. A corrosion resisting alloy containing approximately 5.0% aluminum, 0.01- to 0.5% arsenic and the remainder copper.

5. An alloy of the character described highly resistant to air impingement corrosion and localized pitting and adapted for use in condenser rtubes or the like which contains about 2.0 to 9.0% aluminum, 0.2% arsenic with the balance consisting substantially entirely of copper.

ALAN MORRIS. 

